question on memory barrier

[moreau francis <francis_moreau2000@yahoo.fr>]

Hi,

I'm currently trying to write a USB driver for Linux. The device must be
configured by writing some values into the same register but I want to be
sure that the writing order is respected by either the compiler and the cpu.

For example, here is a bit of driver's code:

"""
#include <asm/io.h>

static inline void dev_out(u32 *reg, u32 value)
{
        writel(value, regs);
}

void config_dev(void)
{
        dev_out(reg_a, 0x0); /* first io */
        dev_out(reg_a, 0xA); /* second io */
}

void config_dev_fixed(void)
{
        dev_out(reg_a, 0x0); /* first io */
        wmb();
        dev_out(reg_a, 0xA); /* second io */
        wmb();
}
"""

In this case, am I sure that the order will be respected ? can gcc remove
the first io while optimizing...If so, does "config_dev_fixed" fix it ?

thanks for your answers,

            Francis


	

	
		
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